I bought the predecessor (450) in 1984 and have done a number of up grades to make it into a 550b. I am in the 1/2 million+ round count and still going strong.
I have 2 suggestions,
1) shell plates, buttons and powder funnels are a mix and match part system. There are only 4 different buttons. So sit down and chart out what cartridges you could ever want to reload and what parts it takes to do that, when you cross off the duplicates, you will only end up with a little over half the number than if you bought the ffull kit every time. (45ACP, 30-06, 270 Win, 280 Rem, 7 & 8 Mauser, 308,7-08, 260 Rem, 358 Win and many more use the same plate and buttons, just different powder funnels. The plates for the 223 Rem family will do about 10 cartridges also, the 30-30 plate, the 44 mag plate, and the belted mag plate will each do several also. That is 4 plates for around 40 cartridges. The powder funnels overlap much the same way.)
2) Buy the 550 parts kit. Then when a part breaks on Thursday night before a 3 day weekend you won't be shut down for a big shooting event. Dillon will replace the parts, but the shipping gets bogged down.
3) Buy brass, bullets, powder and primers whenever and wherever you possibly can! Just don't tell your "friends", or they will use your stash as their store.
4) enjoy!!!
That is only 2, The others are common sense.
Ivan